Nickel-chromium-cobalt alloys



Feb. 1, 1966 Filed Jan s. w. K. SHAW ETAL 3,232,751

NICKEL-CHROMIUM-COBAL'I' ALLOYS 3 Sheets-Sheet 1 K 2.5 a 3.5 4 4.5 s5.5- e as Ho(%/ INVENTORS Feb. 1, 1966 I s. w. K. SHAW ETAL 3,232,751

NICKEL-CHROMIUM-COBALT ALLOYS Filed Jan. 23, 1963 3 Sheets-Sheet 2 I58I80 I92 52 INVENTORS awn-r L/AL re? Keg SHAH By fee/mu: Massey Coax ATrue/v6) Feb. 1, 1966 s. w. K. SHAW ETAL 3,232,751

NICKEL-CHROMIUM-COBALT ALLOYS Filed Jan. 23) 1963 3 Sheets-Sheet 5INVENTORS Res/mow Massey Coo M 9m ,4 WHEY United States 3,232,751NICKEL-CHROMIUM-COBALT ALLOYS Stuart W. K. Shaw, Sutton Coldfield, andReginald M. Cook, Kings Heath, Birmingham, England, assignors to TheInternational Nickel Company, lnc., New York, N.Y., a corporation ofDelaware Filed Ian. 23, 1963, Ser. No. 253,426 Claims priority,application Great Britain, Jan. 26, 1962,

7 Claims. (Cl. 75-171) about 1000 C. under loads of at least about 7long tons per square inch (t.s.i.). Although many attempts were made toprovide alloys having the required characteristics, none, as far as weare aware, was entirely successful when carried into practicecommercially on an industrial scale.

It has now been discovered that by special control and interrelation ofalloying constituents of nickel-base alloys, alloys can be providedhaving the presently required engineering characteristics.

It is an object of the present invention to provide a novel heat-,corrosionand stress-resisting nickel-base I alloy.

Another object of the invention is to provide a novel turbine structuremade of a novel heat-, corrosionand stress-resisting alloy.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a graph showing the interrelation between the molybdenumcontent and the total aluminum plus titanium content required in alloysin accordance with the present invention;

FIG. 2 depicts a graph showing the interrelation be tween the chromiumand molybdenum contents required in alloys in accordance with thepresent invention;

FIG. 3 is a graph showing the interrelation between the titanium andaluminum contents required in alloys in accordance with the presentinvention at one content of molybdenum; and

FIG. 4 is a graph showing the effect of the cobalt content upon thestress-rupture life of alloys in accordance with the invention.

In general the alloys according to the invention contain, in percent byweight, about 0.03% to 0.3% carbon, about 8% to 10.9% chromium, about to13% cobalt, about 2.5% to 6.2% molybdenum, titanium and aluminum inamount such that the sum of the titanium and aluminum contents is about6.6% to 11.5% and the ratio of titanium to aluminum is from 0.2:1 to1.521 by weight, about 0.05% to 0.5% zirconium and about 0.005% to 0.05%boron, the balance, apart from impurities, being nickel. The principalimpurities that may be present are iron, silicon and manganese and thetotal amount of these elements must not exceed 3% and should be as lowas possible. Advantageously, the iron content does not exceed 0.5 thesilicon content does not exceed 0.3% and the manganese content does notexceed 0.3%.

One group of alloys according to the invention contain titanium andaluminum in such amounts that the sum of the titanium and aluminumcontents is about 8.4%

3,232,751 Patented Feb. 1, 1966 to 11.5% and the ratio of titanium toaluminum is from 0.7:1 to 1.5:1 by weight.

The contents of chromium and molybdenum, the total content of titaniumand aluminum, and the ratio of ittanium to aluminum at which the longestlives are obtained in stress-rupture tests at 1020 C. .on the castalloys are interrelated. The interrelation of these elements is shown byFIGURES 1 to 3 of the accompanying drawing.

As the total titanium and aluminum content is increased at the expenseof nickel in a series of alloys of otherwise similar composition, theratio of titanium to aluminum being held constant, the stress-rupturelife at 1020 C. increases to a maximum and then again decreases. In asimilar series of alloys having a different molybdenum content, themaximum stress-rupture life is found to occur at a ditierent totaltitanium and aluminum content, the value of which decreases as themolybdenum content increases within the range 2.5% to 6.2%. Furthermoreit is found that the maximum value of the stress-rupture life in theseries of alloys also depends on the molybdenum content, passing througha maximumat molybdenum contents between 2.5 and 6.2% and falling offsharply when the molybdenum content is below 2.5% or above 6.2%. In thealloys of the invention the titanium and aluminum contents are thereforeso related to themolybdenum content that when the ratio of titanium toaluminum is from 0.721 to 1.5:1 the values of the titanium plus aluminumcontent and the molybdenum content, expressed as percentages by weight,lie within the area ABCDA in FIGURE 1 of the accompanying drawing, andpreferably within the area EFGHE. At these ratios of titanium toaluminum, the minimum (Ti-l-Al) content is 8.4% at a molybdenum contentof 6.2%, as shown in FIGURE 1. At lower ratios of titanium to aluminum,between 0.7 :1 and 0.2: l, we find that the ratio of titanium toaluminum also enters into the relationship between the (Ti-t-Al) contentand the molybdenum content, and the total percentage content of titaniumand aluminum must then be from a minimum of (3.7 Ti/Al)-0.43 (PercentMo)+8.48

to a maximum of (1.6 Ti/Al)0.43 (pfircent Mo)+11.45

The effect of variations in the proportions of titanium and aluminum isclearly shown by FIGURE 3 of the drawings, in which the points representthe compositions of a large number of alloys each of which contained,apart from titanium and aluminum, 0.10% carbon, 10%

chromium, 10% cobalt, 4% molybdenum, 0.1% zir-' conium, and 0.01% boron,the balance, apart from impurities, being nickel. The number beside eachpoint represents the stress-rupture life of the alloy at a stress of 7long tons/square inch (t.s.i.) at 1020 C. determined on cast test-barswithout heat treatment. The outer and inner curves represent the limitsof the regions in which the alloys have lives in excess of 10 hours and60 hours respectively under these conditions. The lines VQ, UR and TS,respectively, represent the Ti:A1 ratios 1.5 :1, 0.7:1 and 02:1, and theline QRSTUVQ encloses Table I Alloy N M0, lltl'ktlli 'li-l- Al, ltilt'vto l lloiuzutlou,

' Pt'l't'tlltrupture. lir. percent.

.3 ll 42 4.2 4 ll) 23'. 0.7 0.5 ltil') 3.0 7 8.5 110 1 2. 1

Alloys Nos. 2 and 3 are in accordance with the invention. while Nos. 1and 4 are not.

The chromium content of the alloys affects both the composition at whichlongest lives are obtained at [020 C. and the level of these lives. Asthe chromium content of the alloys is increased, the molybdenum contentat which the longest lives are obtained at 1020 C. decreases, andaccording to the invention the chromium and molybdenum contents are sorelated as to lie within the area IJKLI in FIGURE. 2 of the accompanyingdrawing.

Most. advantageously the chromium content is not less than 9%, and thealloys have contents of chromium and molybdenum represented by pointswithin the area MNOPM in FIGURE 2 of the accompanying drawing.

The effect of varying the chromium content in a series of alloyscontaining cobalt having optimum contents of titaniunt-t-alt1ttrinum andof molybdenum for each chromium content is shown in Table 11.

Each of the alloys was tested at l020 C. and 7 t.s.i.

Table I1 cc .-r- .c we Alloy (.r, per- 5 Mo, pt-r- 'lH-Al, bite to ilitnuunt nu, Nu. cont. cent. percent. rupture, lir. percent,

2 ll 03 I 4.U 10 4 10 232 l at 5 h ll. 5 ltill l 2.. ti

Apart from cobalt, chromium, molybdenum and titanium+aluminum in theamounts stated, all the alloys of Tables I and It contained 0.1% carbon,0.1% zirconium and 0.01% boron, the balance being nickel and impuritiesand the titanium to aluminum ratio, except where otherwise stated, beingunity.

Alloys Nos. Sand 6 in Table It were not in accordance with theinvention, and it will be seen that the stressrupture life attainablefalls off quite sharply with increasing chromium contents. Although thestress-rupture lives of the best alloys with less than 8% chromium arestill quite good, the resistance of these alloys to oxidation andsulfidation is very poor. Thus the apparent satisfactory life to ruptureof the alloy of Table ll containing 5% chromium is offset by the factthat as the chromium is lowered from 10% to 5%, the oxidation resistanceand the sulfidation resistance of the alloy sutiers greatly as shown inTable 111.

till

crties. This is shown by the graph forming FIGURE 4 of the drawing, inwhich the abscissae are the cobalt contents of a series of alloyscontaining, besides cobalt, 10%

chromium, 4% molybdenum, 5% titanium, 5% aluminum, 0.l% carbon. 0.1%zirconium and 0.01% boron, the balance, apart from impurities, beingnickel, and the ordi hates are their stress-rupture lives in hours at 7t.s.i. and l020 C.

Preferably the cobalt content of the alloys according to the inventionis from 9 to l2%, for example, from 9 to 11%.

The carbon content of the alloys is preferably from 0.05% to 0.25%, thezirconium content not more than 0.20% and the boron content not morethan 0.025%.

An alloy (alloy A) that is particularly suitable for use in the castform has the composition:

10% Cr, 10% Co, 4% Mo, 5% Ti, 5% A1, 0.1% C, 0.1% Zr, 0.01% B, balanceNi and impurities.

Cast alloy specimens of this composition have been found to exhibitstress-rupture lives of over 200 hours under a stress of 7 t.s.i. at1020 C. with elongations at rupture of 5% to 109 and to have anunnotched impact strength (0.45 inch diameter testpiece) at 900 C. of 35ft.-lbs. and a notched impact strength (standard Charpy testpiece) at900 C. of 7.2 ft.-lbs.

Another very suitable alloy (alloy B) has the composition:

l0% Cr. i092 Co. 4% M0. 2.5% Ti, 6.5-7% Al, ().l% C, 01% Zr, 0.01% B,balance Ni and impurities.

Cast alloy specimens of this composition have been found to exhibitstress-rupture lives of over 170 hours under a stress of 7 t.s.i. ati020 C. with clongations of about 9%, and lives of about 100 hours at 6t.s.i. at 1950 C. with clongations oi" about 10%.

The alloys according to the invention may be air melted, but arepreferably melted under vacuum. Whether or not they are vacuum melted,the alloys are advantageously subjected to a vacuum rclining treatmentcomprising holding them in the molten state under high vacuum beforecasting the melt. We prefer to hold the melt at a temperature of 1400 C.to 1600 C. at not more than 100 microns pressure (most preferably notmore than 5 microns) for a period of at least 15 minutes andadvantageously for minutes or more. The duration of the treatmentdepends to some extent on the purity of the ingredients of the melt, alonger time being required when less pure ingredients are employed.

When producing small-casting, for example, turbine blades orstress-rupture testpieces, the alloys are preferably cast under vacuum,but when producing large castings front a melt that has been produced orrefined under vacuum it makes little ditterence to the propertiesobtained whether casting is carried out in vacuum, inert gas or air. Allthe stress-rupture test results referred to in this specification and inthe drawings were obtained on test pieces machined from cast specimensthat had been vacuum cast from vacuum melted material that had beenvacu' 5. um refined for at least 15 minutes at 1500 C. under a pressureof less than 1 micron.

Articles and parts cast from the alloys may be used in the as-castcondition for high temperature service, for example, as rotor blades ingas turbine engines, and no marked improvement in properties is found onsubsequent heat treatment.

The alloys also exhibit useful stress-rupture properties in the wroughtform after solution heating and aging. Generally speaking, solutionheating may be performed at temperatures in the range 1150 C. to 1250 C.for periods between l and 3 hours. Heating at these temperatures forlonger than 3 hours leads to excessive grain growth. Within thistemperature range an upper limit is set by the incipient melting pointof the alloy, and for alloys having a (TH-Al) content of 10% thepreferred solution heating temperature is 1225 C. As the (Ti-t-Al)content of the alloy is increased, the temperature required to take thewhole of the primary gamma-phase into solution also increases, and at(Ti+Al) contents above 11.5% it is impossible to obtain completesolution of this phase below the incipient melting point, so that thestress-rupture properties of the alloy after aging fall 01f. Thestress-rupture properties after age hardening also fall otf as the(TH-Al) content is decreased below 10%, in a similar manner to theproperties of the cast alloys. Aging is preferably etfected by heatingin the range 900 C. to 1100 C. for from 1 to 24 hours, the time requiredde creasing as the temperature is increased and increasing withincreasing section size. The temperatures during aging may be variedwithin the above mentioned range or, if desired, aging may be effectedby cooling the alloy By way of example, a specimen of a wrought alloyhaving the composition:

0.10% C, 10% Cr, 10% Co, 3.5% Mo, 5% Ti, 5% Al,

0.1% Zr, 0.01% B, balance Ni had a life to rupture of 58 hours under astress of 7 t.s.i. at 1020 C. after a heat treatment comprising solutionheating for 1.5 hours at 1250 C. followed by aging at 1000 C. for 6hours. Similar properties are obtained if the aging step comprisesfurnace cooling from the solution heating temperature, e.g., down to1150 C. or 1100 C.

Despite their low chromium content the alloys of the invention haveremarkably good resistance to oxidation at high temperatures.Nevertheless, for use at temperatures above 1000 C. under conditionssuch as are encountered in gas turbine engines involving both oxidationand sulfur attack, articles and parts made from the alloys arepreferably provided with a protective coating, for example, of aluminum.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be undersood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. An alloy for use under high stress at elevated temperatures andcharacterized by a high stress-rupture life, said alloy consistingessentially of, in weight percent, about 0.03% to about 0.3% carbon,about 8% to 10.9% chromium, about 5% to about 13% cobalt, about 2.5% toabout 6.2% molybdenum, about 8.4% to about 11.5% total titanium plusaluminum with the ratio of said titanium to said aluminum being about0.2 to l to about 1.5

to 1, about 0.05% to about 0.5% zirconium, about 0.005% to about 0.05%boron, the balance apart from impurities being nickel, the elementstitanium, aluminum and molybdenum in said alloy being interrelated such0.2 to l to 0.7 to 1 the said ratio is correlated with the percentage ofmolybdenum such that the percentage of total titanium plus aluminum isfrom a minimum of (3.7 Ti/Al) 0.43 X (P rcent Mo) +8.48

to a maximum of (1.6 Ti/Al)--0.43 X(P rcent Mo) +1 1.45

said alloybeing further characterized such that the percentages ofmolybednum and chromium are correlated so as to represent a point lyingwithin the area IJKLI in FIGURE 2 of the accompanying drawing.

2. An alloy as in claim 1 wherein the chromium content is from 9% to10.9%, the correlation of the total titanium plus aluminum percentageand the molybdenum percentage is represented by a point lying within thearea EFGHE in FIGURE 1 of the accompanying drawing and thecorrelation ofthe chromium and molybdenum percentages is represented by a point lyingwithin the area MNOPM in FIGURE 2 of the accompanying drawing.

3. An alloy as set forth in claim 2 wherein the cobalt content is about9% to about 12%, the carbon content is about 0.05% to about 0.25 thezirconium content does not exceed 0.20% and the boron content does notexceed 0.025%.

4. A gas turbine structure made of an alloy as in I peratures andcharacterized by a high stress-rupture life,

said alloy consisting essentially of, in weight percent, about 0.05% toabout 0.25% carbon, about 8% to 10.9% chromium, about 5% to about 13%cobalt, about 2.5% to about 6.2% molybdenum, about 8.4% toabout 11.5%total titanium plus aluminum with the ratio of said titanium to saidaluminum being about 0.2 to 1 to about 1.5 to l, and with the total sumof titanium plus aluminum representing a point falling within the areaQRSTUVQ of FIGURE 3 of the accompanying drawing, about 0.05% to about0.2% zirconium, about 0.005% to about 0.25% boron, the balance apartfrom impurities being nickel, the elements titanium, aluminum andmolybdenum in said alloy being interrelated such that at a ratio oftitanium to aluminum of from about 0.7 to l to about 1.5 to 1 thecorrelation of the percentage of total titanium plus aluminum and thepercentage of molybdenum is represented by a point lying within the areaABCDA in FIG- URE l of the accompanying drawing and at a ratio oftitanium to aluminum of from about 0.2 to 1 to 0.7 to 1 the said ratiois correlated with the percentage of mo-v lybdenum such that thepercentage of total titanium plus aluminum is from a minimum of centagesof molybdenum and chromium are correlated so as to represent a pointlying within the area IJKLI in FIGURE 2 of the accompanying drawing.

6. An alloy for use under high stress at elevated temperatures andcharacterized by a high stress-rupture life of over 200 hours at atemperature of 1020 C. under a cobalt, about 4% molybdenum, about 5%titanium, about 5% aluminum, about 0.1% zirconium, about 0.01% b0- ronand the balance essentially nickel. 7. An alloy for use under highstress at elevated temperatures and characterized by a stress-rupturelife of over 170 hours under a stress of 7 long tons per square inch ata temperature of 1020 C. in the cast condition, said alloy consistingessentially of, in weight percent, about 0.1% carbon, about 10%chromium, about 10% cobalt, about 4% molybdenum, about 2.5% titanium,about 6.5% to 7% aluminum, about 0.1% zirconium, about 0.01% boron andthe balance essentially nickel.

References Cited by the Examiner DAVID L.

U N IT ED STATES PATENTS 9/1960 Brown 75--171 3/1961 Bieber 75-17110/1963 Gittus 75--171 11/1963 Gittus et a1 7517l FOREIGN PATENTS12/1959 Australia.

5/ 1959 Great Britain. 9/ 1955 Great Britain.

RECK, Primary Examiner.

15 WlNST ON A. DOUGLAS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,232,751 February 1, 1966 Stuart W. K. Shaw et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2, line 4, for "it-" read ticolumn 4, line 39, for "1950 C." read1050 C. line 55, for "casting" read castings column 5, line 19, forgamma-phase" read gamma phase column 6, line 49, for "0.25%" read 0 025%Signed and sealed this 7th day of February 1967.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. AN ALLOY FOR USE UNDER HIGH STRESS AT ELEVATED TEMPERATURES ANDCHARACTERIZED BY A HIGH STRESS-RUPTURE LIFE, SAID ALLOY CONSISTINGESSENTIALLY OF, IN WEIGHT PERCENT, ABOUT 0.03% TO ABOUT 0.3% CARBON,ABOUT 8% TO 10.9% CHROMIUM, ABOUT 5% TO ABOUT 13% COBALT, ABOUT 2.5% TOABOUT 6.2% MOLYBDENUM, ABOUT 8.4% TO ABOUT 11.5% TOTAL TITANIUM PLUSALUMINUM WITH THE RATIO OF SAID TITANIUM TO SAID ALUMINUM BEING ABOUT0.2 TO 1 ABOUT 1.5 TO 1, ABOUT 0.05% TO ABOUTR 0.5% ZIRCONIUM, ABOUT0.005% TO ABOUT 0.05% BORON, THE BALANCE APART FROM IMPURITIES BEINGNICKEL, THE ELEMENTS TITANIUM, ALUMINUM AND MOLYBDENUM INSAID ALLOYBEING INTERRELATED SUCH THAT AT A RATIO OF TITANIUM TO ALUMINUM OF FROMABOUT 0.7 TO 1 TO ABOUT 1.5 TO 1 THE CORRELATION OF THE PERCENTAGE OFTOTAL TITANIUM PLUS ALUMINUM AND THE PERCENTAGE OF MOLYBDENUM ISREPRESENTED BY A POINT LYING WITHIN THE AREA ABCDA IN FIGURE 1 OF THEACCOMPANYING DRAWING AND AT A RATIO OF TITANIUM TO ALUMINUM OF FROMABOUT 0.2 TO 1 TO 0.7 TO 1 THE SAID RATIO IS CORRELATED WITH THEPERCENTAGE OF MOLYBDENUM SUCH THAT THE PERCENTAGE OF TOTAL TITANIUM PLUSALUMINUM IS FROM A MINIMUN OF